The pain mediating system in a human consists of two kinds afferent fibers: A-delta and C-fibers. These afferent pain fibers characterized by different physiological parameters, for example, conduction velocity (15-50 ml/s for A-delta fibers and <2 m/s for C-fibers). These two fiber types project to different parts of the dorsal horn of the spinal cord. In addition, stimulation of each kind of nociceptors evokes different type of sensation: A-delta fibers mediate first (sharp, pin-prick) pain sensation; C-fibers mediate the sensation of second pain usually perceived as burning sensation.
Dysfunction of pain- and sensory-mediated systems often accompanies various neurological disorders as well as other pain syndromes of unknown etiology. Therefore, selective activation and identification of the response may offer very significant opportunity for proper diagnostic and treatment in pain patients. The most popular tool for the evaluation of A-delta functioning is radiant heat laser stimuli that evoke pin-prick sensation (e.g., user response) and well defined potential on EEG recording. However, selective activating with subsequent recording for the evaluation of C-fibers activity is apparently more difficult. Some existed methods for the selective C-fibers activation are based on laser stimulation following the ischemic block of A-delta fibers; applying laser stimuli on very tiny cutaneus surface areas (d=0.5 mm) using special lens; or by stimulating skin surface through special filter. These methods, however, have not found widespread clinical use, possibly due to their complexity and/or poor sensation generation quality.
Peltier elements have been used for heat and/or cold stimulating a body portion for evaluating nervous sensitivity, for example, as described in WO 00/23030, the disclosure of which is incorporated herein by reference.
An article in Pain 100 (2002) 281-290, the disclosure of which is incorporated herein by reference, describes a cold-stimulation device.
During brain surgery there is a general difficulty of determining if tissue about to be damaged serves a crucial brain function.
In surgical procedures, patients are typically given a mixture of drugs to have the following three effects: anesthesia (loss of consciousness), pain reduction and immobilization. Due to the difficult in determining if the correct effect has been achieved, there exists a problem of patients which are immobilized but are conscious and/or feel pain during surgery. Even if not conscious, pain can cause an increase in sensed or even chronic pain after surgery,